The present invention relates to galvanomagnetic devices.
The magnetic sensitivity of virtually all galvanomagnetic sensors such as Hall generators, magnetoresistors (MRs), etc. are temperature dependent. It is well known in the art that the resistance modulation of galvanomagnetic sensors can be employed in position and speed sensors with respect to moving ferromagnetic materials or objects (see for example U.S. Pat. Nos. 4,835,467, 4,926,122, and 4,939,456).
The shortcoming of galvanomagnetic sensors is their temperature sensitivity. They have a negative temperature coefficient of resistance and their resistance can drop as much as 50% when heated to 180 degrees Celsius (180xc2x0 C.). Generally, this led to the use of MR devices in matched pairs for temperature compensation. Additionally, it is preferable to drive MR devices with current sources since, with the same available power supply, the output signal is nearly doubled in comparison with a constant voltage source.
To compensate for the MR resistance drop at higher temperatures, and thus, the magnitude decrease of the output signal resulting in decreased sensitivity of the MR device, it is also desirable to make the current of the current source automatically increase with the MR temperature increase. This is shown in U.S. Pat. No. 5,404,102 in which an active feedback circuit automatically adjusts the current of the current source in response to temperature variations of the MR device.
The temperature dependence of galvanomagnetic sensors makes it very difficult, if not even impossible, to design devices having the desired properties over extended temperature ranges such as some of the present automotive ones from xe2x88x9240xc2x0 C. to nearly 200xc2x0 C. Currently employed techniques of doping decrease the magnetic sensitivity along with the sought after decrease in temperature sensitivity. In the limit, using the present doping approach one might obtain devices insensitive to temperature, but also practically insensitive to magnetic fields.
It should be noted that the present invention differs from U.S. Pat. No. 5,184,106 to Partin and Heremans in that U.S. Pat. No. 5,184,106 gave a recipe for maximum electron mobility, whereas the present invention trades off the magnitude of the mobility for increased temperature stability.
What is needed is a method to compensate for the temperature dependence of galvanomagnetic sensors.
We discovered that for wide temperature ranges one can tailor the properties of galvanomagnetic devices by controlling doping types and levels, film thickness, alloy composition, device geometry, etc. The present invention involves, generally, the making of galvanomagnetic device layers with a desired combination of properties in specific temperature ranges and magnetic field ranges and combining them into a single composite galvanomagnetic device having the desired properties in an extended temperature and magnetic field range. The process of combining would result in a single die with layers of different properties.
More specifically, the present invention addresses magnetoresistors and Hall effect devices, also known in the art as Hall effect plates or Hall plates. Further, the present invention describes a recipe to manufacture magnetoresistors and Hall effect devices utilizing semiconductors such as indium antimonide (InSb) with a magnetic field sensitivity that is independent of temperature.
It is known that indium-antimonide magnetoresistors and Hall effect devices made out of material doped with rare earth elements, such as erbium or samarium have less temperature dependence to their magnetic sensitivity. Advantages of the present invention thereover include:
1. indium-antimonide magnetic field sensors have a larger temperature range than silicon-based Hall sensors, which are essentially limited to temperatures slightly above 150 degrees centigrade; and
2. the present recipe is easier to manufacture than the rare earth doped indium antimonide magnetic field sensors, because it uses only chemicals that are conventional in the fabrication of eptitaxial compound semiconductors.
Accordingly, it is an object of the present invention to reduce the temperature sensitivity of galvanomagnetic devices using the above recounted solutions.